An involuntary jerking or bouncing of an eyeball may be noticed under the influence of alcohol or certain other central nervous system depressants. Such involuntary movements, called nystagmus, may be a result of alcohol caused hindering of the ability of the brain to correctly control eye muscles. Horizontal gaze nystagmus (HGN) refers to a lateral or horizontal jerking when the eye gazes to the side. With an increase of blood alcohol level, the degree of hindering becomes greater; thus the jerking becomes more noticeable. The degree of HGN may be assessed to detect blood alcohol level.
Conventional horizontal and/or vertical gaze nystagmus tests are part of field sobriety tests used by law enforcers and medics to assess alcohol impairment of a person. However, accuracy and reliability of conventional HGN tests are subject to challenge. Device-assisted tests may be influenced by hand and/or head shaking and other factors.
Moreover, conventional methods are intended for policemen and medics, rather than users willing to assess own blood alcohol level.